CHARACTERISTICS OF SHALLOW RAIN-IMPACTED FLOW OVER SMOOTH BED

An understanding of the effect of rainfall on the characteristics of s hallow flow is needed for the proper modeling of the physical processe s related to erosion and sedimentation. In this study, the turbulence characteristics of shallow rain-impacted flow over a smooth bed were i nvestigated using a fiber-optic laser Doppler velocimeter and a specia lly designed artificial raindrop simulator. An empirical formula was d erived to predict the variation of momentum correction factor beta wit h the parameters related to the flow and the rainfall characteristics. Statistical correlations were developed successfully to predict the d istributions of both the longitudinal and the vertical turbulence inte nsities for rainfalls with different intensities and raindrop diameter s. The statistical characteristics of the Reynolds stress under differ ent rainfall conditions also were analyzed. Analysis of the energy spe ctrum of the longitudinal velocity component indicated that the energy for the largescale eddies (low frequencies) was increased significant ly because of the mixing effect of the raindrop impact for the region near the water surface.